Re: [BUG][PATCH] arm64: bti: fix BTI to handle local indirect branches

From: Jeremy Linton
Date: Mon Oct 05 2020 - 15:24:53 EST

Hi,

On 10/5/20 1:54 PM, Ard Biesheuvel wrote:
On Mon, 5 Oct 2020 at 20:18, Jeremy Linton <jeremy.linton@xxxxxxx> wrote:

The AES code uses a 'br x7' as part of a function called by
a macro, that ends up needing a BTI_J as a target.

Could we instead just drop the tail call, i.e, replace it with a ret
and do a 'bl' after it returns? The indirect call does not really
serve a purpose here anyway

Yes, that is an option, it adds an extra ret. Which probably doesn't mean much in most cases. I assumed this code was optimized this way because it mattered somewhere.



Lets
define SYN_CODE_START_LOCAL() for this and replace the
SYM_FUNC_START_LOCAL with a SYM_FUNC_CODE_LOCAL in the AES block.
^ That should have read SYM_CODE_START_LOCAL.

Without this kernels compiled with the aes_neon_bs will OOPS
at boot.

Bad mode in Synchronous Abort handler detected on CPU1, code 0x34000003 -- BTI
CPU: 1 PID: 265 Comm: cryptomgr_test Not tainted 5.8.11-300.fc33.aarch64 #1
pstate: 20400c05 (nzCv daif +PAN -UAO BTYPE=j-)
pc : aesbs_encrypt8+0x0/0x5f0 [aes_neon_bs]
lr : aesbs_xts_encrypt+0x48/0xe0 [aes_neon_bs]
sp : ffff80001052b730
x29: ffff80001052b730 x28: 0000000000000001
x27: ffff0001ec8f4000 x26: ffff0001ec5d27b0
x25: ffff0001ec8f4000 x24: ffff80001052bc00
x23: 0000000000000018 x22: 000000000000000a
x21: ffff0001ec5d2100 x20: ffff0001ec8f4080
x19: ffff0001ec8f4000 x18: 0000000000000004
x17: 0000000000000000 x16: ffffadb4db85d310
x15: 0000000000000200 x14: 0000000000000010
x13: 0000000000000200 x12: ffff0001ec5d2100
x11: 000000000000000a x10: 0000020000200000
x9 : ffffadb4db7e7488 x8 : 0000000000000000
x7 : ffffadb4614fb110 x6 : 0000000000000000
x5 : ffff80001052bc00 x4 : 0000000000000020
x3 : 000000000000000a x2 : ffff0001ec5d2100
x1 : ffff0001ec8f4000 x0 : ffff0001ec8f4000
Kernel panic - not syncing: bad mode
CPU: 1 PID: 265 Comm: cryptomgr_test Not tainted 5.8.11-300.fc33.aarch64 #1
Call trace:
dump_backtrace+0x0/0x1c0
show_stack+0x24/0x30
dump_stack+0xc0/0x118
panic+0x144/0x358
arm64_serror_panic+0x0/0x98
el1_sync_handler+0x60/0x110
el1_sync+0xb4/0x180
aesbs_encrypt8+0x0/0x5f0 [aes_neon_bs]
__xts_crypt+0xb0/0x2dc [aes_neon_bs]
xts_encrypt+0x28/0x3c [aes_neon_bs]
crypto_skcipher_encrypt+0x50/0x84
simd_skcipher_encrypt+0xc8/0xe0
crypto_skcipher_encrypt+0x50/0x84
test_skcipher_vec_cfg+0x224/0x5f0
test_skcipher+0xbc/0x120
alg_test_skcipher+0xa0/0x1b0
alg_test+0x3dc/0x47c
cryptomgr_test+0x38/0x60
kthread+0x11c/0x120
ret_from_fork+0x10/0x18
SMP: stopping secondary CPUs
Kernel Offset: 0x2db4cb7e0000 from 0xffff800010000000
PHYS_OFFSET: 0xffffcf2440000000
CPU features: 0x7e0152,20c02020
Memory Limit: none
---[ end Kernel panic - not syncing: bad mode ]---

Fixes: commit 0e89640b640d ("crypto: arm64 - Use modern annotations for assembly functions")
Signed-off-by: Jeremy Linton <jeremy.linton@xxxxxxx>
---
arch/arm64/crypto/aes-neonbs-core.S | 8 ++++----
arch/arm64/include/asm/linkage.h | 6 +++++-
2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/crypto/aes-neonbs-core.S b/arch/arm64/crypto/aes-neonbs-core.S
index b357164379f6..76de87ee80e1 100644
--- a/arch/arm64/crypto/aes-neonbs-core.S
+++ b/arch/arm64/crypto/aes-neonbs-core.S
@@ -428,7 +428,7 @@ SYM_FUNC_START(aesbs_convert_key)
SYM_FUNC_END(aesbs_convert_key)

.align 4
-SYM_FUNC_START_LOCAL(aesbs_encrypt8)
+SYM_CODE_START_LOCAL(aesbs_encrypt8)
ldr q9, [bskey], #16 // round 0 key
ldr q8, M0SR
ldr q24, SR
@@ -488,10 +488,10 @@ SYM_FUNC_START_LOCAL(aesbs_encrypt8)
eor v2.16b, v2.16b, v12.16b
eor v5.16b, v5.16b, v12.16b
ret
-SYM_FUNC_END(aesbs_encrypt8)
+SYM_END(aesbs_encrypt8)

.align 4
-SYM_FUNC_START_LOCAL(aesbs_decrypt8)
+SYM_CODE_START_LOCAL(aesbs_decrypt8)
lsl x9, rounds, #7
add bskey, bskey, x9

@@ -553,7 +553,7 @@ SYM_FUNC_START_LOCAL(aesbs_decrypt8)
eor v3.16b, v3.16b, v12.16b
eor v5.16b, v5.16b, v12.16b
ret
-SYM_FUNC_END(aesbs_decrypt8)
+SYM_END(aesbs_decrypt8)

/*
* aesbs_ecb_encrypt(u8 out[], u8 const in[], u8 const rk[], int rounds,
diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h
index ba89a9af820a..92c81ae8ac1e 100644
--- a/arch/arm64/include/asm/linkage.h
+++ b/arch/arm64/include/asm/linkage.h
@@ -11,7 +11,8 @@
* set the architecture version to v8.5 we use the hint instruction
* instead.
*/
-#define BTI_C hint 34 ;
+#define BTI_C hint 34 ;
+#define BTI_JC hint 38 ;

/*
* When using in-kernel BTI we need to ensure that PCS-conformant assembly
@@ -42,6 +43,9 @@
SYM_START(name, SYM_L_WEAK, SYM_A_NONE) \
BTI_C

+#define SYM_CODE_START_LOCAL(name) \
+ SYM_START(name, SYM_L_LOCAL, SYM_A_ALIGN) \
+ BTI_JC
#endif

/*
--
2.25.4